Q37E

Question

The 1H NMR spectrum of bullvalene at 100 °C consists only of a single peak at 4.22 d. Explain.

Step-by-Step Solution

Verified

Answer

Bullvalene readily undergoes Cope rearrangement and tautomerism, thus all carbon atoms and hydrogen atoms appear equivalent on the NMR timescale.

The interconversions can be represented as:

1Step 1: About Bullvalene

Bullvalene(C₁₀H₁₀) is a hydrocarbon that has a cage-like structure formed by the fusion of one cyclopropane and three cyclohepta-1,4-diene rings. It a fluxional moleculewhich means it undergoes dynamics so that some or all its atoms interchange between symmetry equivalent positions.

2Step 2: Why Bullvalene showed only one peak in 1H NMR

It is an unusual organic molecule as the C−C and C=C bonds form and break rapidly on the NMR timescale. The bullvalene molecule has a cyclopropane platform on which three vinyl arms are joined along with a methine group. Due to this arrangement, it readily undergoesCope rearrangement and tautomerism, thus all carbon atoms and hydrogen atoms appear equivalent on the NMR timescale.

The interconversions can be represented as:

Q36E

Q38E

Other exercises in this chapter

Q35E

Ring-opening of the trans-cyclobutene isomer shown takes place at much lower temperature than a similar ring-opening of the cis-cyclobutene isomer. Explain the

View solution

Q36E

Photolysis of the cis-cyclobutene isomer in Problem 30-35 yields cis-cyclododecaen-7-yne, but photolysis of the trans isomer yields trans-cyclododecaen-7-yne. E

View solution

Q38E

The following rearrangement was devised and carried out to prove the stereochemistry of [1,5] sigmatropic hydrogen shifts. Explain how the observed result confi

View solution

Q39E

The following reaction is an example of a [2,3] sigmatropic rearrangement. Would you expect the reaction to be suprafacial or antarafacial? Explain.

View solution